High-temperature steel



J y 1952 P. A. JENNINGS 2,602,738

' HIGH-TEMPERATURE STEEL Filed Jan. 50, 1950 C. 0.05%7.50% CB: 72%30% 5/. 0.45% MAX.

N. 0,06% 040% FE. EAL/INCA INVENTOR 7 PAUL A.- JEN/Vl/VGJ.

H/S ATTORNEY Patented July 8, 1952 Serial No. 762,863' filed July 23, 1947, also'abandoned,--and the invention relates to high temperature stainless steel articles, especially to articles in the form-of valves, valve parts and other internal combustion engine components intended for use' while pheres. I Amongthe objects of my invention isthe provision of strong, tough and durable 'austenitic stainless steel valves and otherinternal c'om bustion engine components forelevatedte'mper ature use, which steel-products, in view of the excellent properties of the particular steel employed function in a highly satisfactory manner in such fields as passenger car, truck, aircraft, diesel and marine vessel engine use, and which offer great hardness at the high temperatures encountered in use, and substantial resistance, in the heated condition, to hot corrosive atmospheres such as those containing the combustionproducts of anti-knock gasoline illustratively of the tetra-ethyl lead variety.

Other objects of my invention in part will be obvious and in part pointed out more fully hereinafter.

The invention accordingly consists in the combination of elements, composition of materials andfeatures of products, and in the relation of each of the same to one or more of the others as'described herein, the scope of the ap lication of which is indicatedin the following claims. The single figure of the accompanying drawing hot in corrosive atmosrepresents av specific product and steel composition thereof falling within the scope'of my invention.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that a great variety of heretofore known valves and valve parts intended for use as operating components of internal combustion engines or the like have become obsolete for such reasons as increased engine temperatures incident to greater engine power and speed. In average passenger cars, for example, the temperatures encountered by the valves frequently are as high as'700'F- or more at the fuel intake position, and as high as 1100 F. to 1450 F. or more at the exhaust position. These temperatures ordinarily are even burning away the metal.

Hr MPERATURE' STEEL Paul J ennings, Baltimore, l assignor to Armco ,Steel Corporation, a corporati ofghio I Applicatim January 3 1950; Serial tic-1141291 s. (o1.75,- 12g f f' MED higher in truck, bus, marine vessel or aircraft engines, especially in the region where the'exhaust valves operate.

Low-alloy steel valves, for example, T which formerly operated satisfactorily in internal combustion engines now arefound in most instances to be unacceptable, and particularly so on the exhaust side 'of these engines. The valves usually burn orwarp very quickly-at the'high operating temperatures, thus impairing engine emcien'cy and requiring frequent replacement. While hot,'the working parts commonly develop oxide scale which detriment'ally' affects proper seating. In turn, failure of the valve to seat properly allows leakage or blow-by ofthe hot gases; thus increasing the valve temperature and An example of this type valve is one containing about 0.45% carbon,

8 .50% "chromium; 3.25%;Si1i60ll, and the 'remainder substantially all iron. v

Also, most of the low-alloy steel valves, including those having the composition just noted, are extremely susceptible to active corrosive attack by leaded fuels and particularly by the hot combustion products of these fuels. J There are antiknock fuels containing lead on the market, which,

when: consumed, not only exert a ruinous effect upon steel valves of low-alloy content, but a great majority of relatively high-alloy. steel valves and parts likewise suffer great detriment and rapid deterioration'when exposed to the fuel combustion products. 1

A number of stainlesssteel valves, and valves made of other high-alloy metal, for example, have been introduced for better serving'present-day needs. Some of these are of ferritic grade steel. Others are martensitic. 'In some, ,there is a high-silicon content and, as a result, they i enjoy adequate scaling resistance. Unfortunately, however, they have poor resistance. to :lead compounds and are decidedly inferior in matters of hot hardness and stretch resistance under certain operating conditions.

:There are still other valves in the prior art, these being of austenitic chromium-nickelstainless steel grade. The amounts of silicon in the conventional austenitic steel products range .from about 0.50%.120 4.0% or more. vIn general, the austenitic steel valves have-a more favorable lattice structure for resisting stress-rupture and creep at elevated temperatures than do the ferritic or martensitic products. It is also true that the relatively high-alloy content of the chromium-nickel austenitic steel favors resistanceto scaling from heat at engine temperatures. ,A

cordingly, is the provision of high temperature heat-resistant, corrosion-resistant stainless steel valves, valve parts and internal combustion engine components having substantial strength,

at the temperatures of use, which are substantially free of phase transformation, are hot hard, resist stretch, and efiiciently and'reliably resist oxidation in the presence of heat and leaded fuel combustion products;

Referring now more particularly to the practice of myinvention,- I providelow-silicon, austenitic chromium-nickel-manganese stainless steel internal combustion engine valves, valve parts, and any of other internal combustion engine components made of the steel, illustratively intake or exhaust poppet valves, stems, heads, springs, casings, claddings, linings or .surfacings. In preferred compositiom, my products include about 0.08% to 1.50% carbon, from 12% to chromium, 2% to nickel, amounts of manganese ranging from 3%. lip-12%, with the silicon content not exceeding 0.25%, and the remainder substantially all ,iron. Preferably, for desired hardness at the high temperatures encountered in actual use, the carbon content amounts to some 0.40% to 1.50%. By keeping an appreciable manganese content; in the steel, and the silicon content below about the 0.25 figure, I find sharp improvement in resistance of the steel products to corrosion and attack by products of combustion resulting'from' the burning of leaded fuel. At about 0.15% silicon and on down-to 0.10% or less, this improvement is even more pronounced, and the hot-hardness is not adversely afiected. Both the hot-hardness and corrosionresistance are even more favorable where the carbon exceeds about 0.40% and the silicon ranges from about 0.15% on down substantially to zero in amount. The smaller quantities of silicon accordingly are usually preferred.

The inclusion of manganese results from my discovery that nickel in steels of the stainless grade often has an adverse effect upon the corrosion resistance ofvalve products while the latter operate in thepresenceiof hot lead compounds. By supplanting a substantial quantity of thenickel ordinarily required for providing a steel of austenitic quality with manganese'an austenitic balance steel is had and the adverse effect of nickel upon corrosion resistance in the combustion products of leaded fuels is importantly dispelled. Moreover, it seems that the steel of high manganese content has a greater solubility for carbon andas such permits greater hot hardness as higher temperatures are achieved.

On occasions, I use the element nitrogen in amounts up to.about.0.30%, or-even'upto about 0.40%, as a substitute for an equivalent amount of carbon or nickel in the steel; The nitrogen when used, serves the function of increasing'the hot-hardness of the steel; It'also serves as. a partial substitute for other austenite-forming elements to maintain the austenitic balance. Also, at times, Isubstitute the element cobalt in discreet amounts for one or more of theZausteniteforming elements, manganese, nickel and carbon. There are occasions too where my'stainless steel products include in the alloy composition thereof, as for special purposes, oneprmore suchelements as molybdenum, titanium, coluinblum, tungsten, vanadium, copper, tantaalum, aluminum, zirconium, or the like, ranging f om quite, sma amountsto substantial amounts n a t-inconsisten with properties desired;

The stainless steel valves, valve p rts and engine components which I provide hav sulphur content which may be some quantity b about 0.04%, or even as much as 0.2% or larger quantities of sulphur, and especial the effect of the low-silicon contentnin promot g resistance to attack by the combustion products of leaded gasolines and the like. The larger quantities of sulphur, say those beyond about 0.04%, usually improve the machining'rproperties' of the steel. Amounts of sulphur much-beyond- 0.2 0% often introduce not working difiiculties with certain of the austenitic steels WhlQh- I eI nploy; also, the rateof. improvement of resistance to lead oxide corrosion usually decreases for these greateramounts -The'phosphorus content of my products preferably isbelowaabout doe The particular amounts of such; elements as chromium, nickel andmanganese present in the internal combustion engine products -w, hich I provide assure excellent heat; resistance and resistance to oxidation at the high temperatures encountered. Also, the inclusion of manganese, and the restriction of silicon tothe critically small amounts indicated, contribute-to scorrosion-resistanceof the products in the;c ombusti0 ;-products of leaded fuels, aswhere the steel takes the form ofanexhaust-valve orpart exposed to aircraft, truck or passenger, car engine exhaust gases. By virtue' otthe-austenitic quality of the steel, my valve products suffer substantially no phase transformation during heating and cooling cycles and, accordingly,- are free of volume changes and difiiculties often; following upon change of phase; The valves are strong,.tough and hot hard at the-highv temperatures encountered. They resist scaling; Warping and cracking at full temperature and upon being cooled and reheated. 1 H I To illustrate the efiect of silicon contenton the resistance to corrosion of chromium-nickel.- manganese stainless steels by lead compounds; attention is directed to Table I below. i This table represents a 21- 3-10 chromium-nickel- -manganese steel subjected to mol-t-en lead oxide at 1675v F. for one hour,.and. to hot-hardness-tests at 1400 F. The resistance to molten lead oxide is given in terms of weight-loss in grams per square decimeter perhour, and thefhot-hardness in terms of Brinell values using a coldball penetrator. d

- TABLE I Influence. of silicon on ,corrosio' rreresz'stance to molten-lead oxide of121-3 10 chromium-nickelmanganese steel (clay crucible) .-Wt. .Hot Sample Q Cr N Mn Si" Loss Hardness r l675 F.l400..F.'

4. 2 .28 0.42- 3:02; 3.0 not use 8.1 s

1 Nominal composition.-

Corrosion by molten lead oxide is found to be even more pronounced where a magnesia crucible is employed. A series of samples of 21-3-10 chromium-nickel-manganese steels of differing silicon contents were subjected to molten lead oxide at 1675 F. for one hour in a magnesia crucible with corrosion-loss results as given in Table II below:

TABLE II Influence of silicon on corrosion-resistance to molten lead Oxide of 21-31-10 chromiumniclcel-mang'anese steel (magnesia crucible) The data presented above shows the highly critical character of silicon content. Where the silicon content exceeds about 0.25%, corrosion by lead oxide rapidly increases. Minimum corrosion is had where the silicon content is 0.15% or less, preferably about 0.10% or less, although certain beneficial properties are had in the 21-3-10 chromium-nickel-manganese steel even wherethe silicon content is up to 0.45% as noted in Table I above and in my parent application, Serial No. 786,976.

The effect of a purposeful nitrogen addition upon hot-hardness is demonstrated by the comparative figures given in Table III below. The samples analyse approximately 21% chromium, 4% nickel, 9% manganese, 0.10% silicon, .60% carbon, with varying nitrogen contents and remainder iron. All samples were heated at about 2150 F. for one hour, then water-quenched, and finally aged at a temperature of about 1350 F. to 1400 F. The hot-hardness tests were made with a cold ball penetrator at 1400 F. and are reported in Brinell. The corrosion tests were made by immersing the samples in molten lead oxide contained in a new magnesia crucible at a temperature of 1675 F. for one hour, the weight loss being reported in grams per square decimeter.

ance to lead amide of chromium-niclceZ-manganese steel Hot Wt Sample 0 Cr Ni Mn Si N Egg Loss C. 66 21. 41 3. 13 10.10 36 none 121 D 21. 59 4. 12 8. 28 42 none 110 1 Nominal composition.

In Table m, it is noted that sample K, with nitrogen in the amount commonly found in stainless steel (up to about 0.05 has a hot-hardness of about Brinell. Where substantial quan tities of nitrogen are introduced, the hardness substantially increases. For example, with a nitrogen content of about 0.10%, sample L, the hardness amounts to 152, with 0.19% and 0.23% nitrogen, samples M and N, it is 161, and with 0.27%, sample 0 it is 170. Nitrogen, therefore, clearly increases the hot-hardness of my steel, and this without sacrifice of the corrosionresisting properties.

Thus it will be seen that in this invention there are provided low-silicon austenitic chromiumnickel-manganese stainless steel articles and products, in which the various objects noted hereinbefore together with many thoroughly practical advantages are successfully achieved. It will be seen that the products are well suited for resisting corrosion in the presence of combustion products of leaded fuels.

While certain of the articles which I provide take the form of internal combustion engine valves, valve parts and other internal combustion engine components, it will be understood that certain advantages of the invention are had from other products of the low-silicon steel, among which are high-temperature gas turbine nozzles, turbine parts adjacent to the nozzle, and any of a variety of supercharger components.

As many possible embodiments may be made of my invention, and as many changes may be made in the embodiment hereinbefore set forth, it will be understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

I claim:

1. Austenitic stainless steel having a hardness exceeding 145 Brinell at a temperature of 1400 F. and substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about .08% to 1.5% carbon, 19% to 23% chromium, 2% to 5% nickel, 7% to 11% manganese, .06% to .40% nitrogen, silicon not exceeding 0.15%, 0.04% to 0.20% sulphur, and the remainder substantially all iron.

2. Austenitic stainless steel having a hardness exceeding 145 Brinell at a temperature of 1400 F. and substantial resistance to corrosion in the presence of leaded fuel combustion products, and containing about .08% to .7% carbon, 19% to 23% chromium, 3% to 6% nickel, 7% to 11% manganese, .1% to 4% nitrogen, silicon not exceeding 0.25%, 0.15% to 0.20% sulphur, and the remainder substantially all iron.

3. Austenitic stainless steel internal combustion engine exhaust valves comprising approximately .08% to .7% carbon, 19% to 23% chromium, 2% to 6% nickel, 3% to 12% manganese, .06% to .40% nitrogen, silicon not exceeding 0.45%, sulphur 0.04% to 0.15%, and the remainder substantially all iron.

PAUL A. JENNINGS.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,438,824 Rich Mar. 30, 1948 2,471,080 Post l May 24, 1949 2,495,731 Jennings Jan. 31, 1950 

1. AUSTENITIC STAINLESS STEEL HAVING A HARDNESS EXCEEDING 145 BRINELL AT A TEMPERATURE OF 1400* F. AND SUBSTANTIAL RESISTANCE TO CORROSION IN THE PRESENCE OF LEADED FUEL COMBUSTION PRODUCTS, AND CONTAINING ABOUT .08% TO 1.5% NICKEL, 7% TO 11% 23% CHROMIUM, 2% TO .40* NITROGEN, SILICON NOT MANGANESE, .06* TO .40% NITROGEN, SILICON NOT EXCEEDING 0.15%, 0.04% TO 0.20% SULPHUR, AND THE REMAINDER SUBSTANTIALLY ALL IRON. 